In the field of digital video processing, forensic watermarking, also called fingerprinting, is a common technique to mark the data processed by a receiving device. It is a way to trace the content if the latter is found on Internet for example, without protection. A first approach is to embed a fingerprint at broadcast side. The server carefully combines secret information (for example copyright information) with the video content in order to hide it into the content so that the receiver can extract back the information for authentication/owner proofing of the content. Another approach is to incorporate the secret at the receiving device side by adding a mark specific to an identification of the receiving device; If a receiving device is a source of illegal redistribution, its individual mark can be extracted and the device itself is clearly identified.
Inserting information into video content is a complex process, where invisibility without compromise on the mark's robustness is the main target. In some cases, due to the insertion mechanism, it may be impossible to reach a perfect invisibility.
Video watermarking techniques are disclosed for example in document US2005/0265576A1 which discloses a video watermarking method and a video content protecting method and apparatus. The method includes detecting scene transition in a video sequence, calculating an image complexity in a scene using one or more frames included in the scene and determining a watermark embedding strength for the scene, and embedding a watermark into the video sequence according to the watermark embedding strength. The watermark thus embedded is invisible.
Document US2004/0008864A1 discloses a method of embedding information in a media stream. The method includes steps of selecting a set of locations within that media stream to embed information, selecting a set of possible alterations to make at those locations, and making a subset of the possible alterations. The set of locations and possible alterations is herein sometimes called a “watermark.” The subset of actual alterations that are made is herein sometimes called a “fingerprint.” The method determines a set of locations at which there are alternative versions of the same media stream, such as one being the original and one being an alternative version of the same media stream (alt-movie). More than one alt-movie or alt-block can be defined for each location in order to permit more than one bit of information to be embedded at each location. Thus, each such location can embed one or more bits of information, the embedded bits being responsive to whether the original movie or the alt-movie is selected for that location. In a preferred embodiment, the method includes noting those blocks at which an alt-block can be selected, and selecting the particular alt-block at each block in response to a random or pseudorandom effect. This type of effect may help a fingerprint resist attacks that attempt to study the run-level codes in order to “undo” the fingerprint. It may also help to spread the watermarking over a relatively large range of spatial frequencies of the content, further diminishing visible effects while also helping to resist attacks.
Fingerprinting techniques recently become more and more attractive as a complementary protection to the scrambling/encrypting techniques. While the latter can secure a pay-content over a delivery network up to but not farther than the final user terminal, fingerprinting continue to protect the content (in a reactive way) for the whole lifetime of the content at a predefined acceptable quality.
However, although achieving vivid performances, the fingerprinting technology still faces the following problems:                Generally speaking, an invisibly inserting method is relatively fragile against various type of content-transformation either intentional or not;        Inserting an invisible mark requires rather a complex detection process, which is not always feasible in some extreme cases;        With inserting a visible mark to avoid the above drawbacks, honest consumers often suffer from disturbing degradation of the content-quality, which can become harmful to the image or reputation of the service provider.        